later. >> once the person has the infection, and if the fection becomes severe, the individual patient can experience lasting and permanent brain damage. >> reporter: so, if you've been bitten, how do you know if you have west nile, if you're one of those rare dangerous cases? the vast majority, 80%, won't have any symptoms. their bodies fight off the disease. for another 19%, the worst symptoms are mild, headaches, fever, nausea. but for less than 1% of people with west nile, severe symptoms, convulsions, paralysis, possibly even death. salvador is out setting traps, hoping the airlierial assault swatted down the danger. >> if there's less mosquitoes, good news. >> reporter: mosquito abatement programs are one of the most effective ways to battle this, but they're threatened by budget cuts.